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Here is the Q&A you are looking for.
Bob Johnson
Q: A couple of months ago you spoke of setting rod and main bearings to 0.001" while using 0.005" shims. Is this possible? Claude Chambers Lone Jack, MO
A; No. Most of the rod and main shims you buy now for the model A are a sandwich of six or more identical 0.003", 0.004" or 0.005" shims stuck tightly together. With a sharp knife, you can peel away a shim at a time. Except where you are boring out new bearings with the shims in place, it is almost impossible to arrive at a 0.001" clearance when using shims this thick. For this reason, never throw away an old shim! With an assortment of shim thicknesses, a 0.001" clearance can generally be worked out.
Adjusting your rod and main bearing clearances isn't as difficult as it might seem. Here are a few tips:
(1) Determine approximately how much shim thickness is going to be required for proper bearing clear-
ance. Be sure that an equal thickness of shims is on each side of the bearing. Try not to **** the cap by using more shim thickness on one side than the other.
(2) Hopefully, you will have 10 or more thousandths of shims on each side of the bearing. If you have an assortment of 0.003", 0.004" and 0.005" shims, you can easily effect a 0.001" change.
(3) Keep all the bearing caps loose except the one you are adjusting.
(4) Although plastigage is a great help, it is not the final answer to proper bearing adjustment. Bearing "drag" is the best final criteria.
(5) Using the plastigage as a tool, adjust shims as necessary to obtain a 0.001"- 0.0015" bearing clearance. The clearance is seldom precisely the same across the entire bearing. It is unwise to go below 0.001" bearing clearance unless it represents an isolated "high spot" in the babbitt.
(6) Plastigage readings are not
dependable for clearances of less than 0.001". If the clearance is less than 0.001", plastigage can actually dent the babbitt. Try to guard against this.
(7) Check the torque required to turn the crank shaft after each adjustment. All caps should be loose except the one you are adjusting. The required torque should be "about" the same for each rod and slightly more for each main. With new rings, most of the torque will be to overcome ring drag. Loosen the cap after adjustment and go on to the next one. After all bearings have been adjusted, torque the nuts on each bearing cap. With all caps tight and using a crank or a torque wrench on the ratchet nut, the crank shaft should turn "hard" on a newly rebuilt engine and with some effort on a used engine.[/QUOT[/B]
That was indeed very kind of you! I’m sure you can expect a six pack in the mail ! Wayne
